Low-dimensional nanomaterial saturable absorbers for ultrashort-pulsed waveguide lasers

A wide range of saturable absorbers composed of novel low-dimensional nanomaterials were fabricated, and their linear and nonlinear optical properties were characterized. Furthermore, their suitability for ultrashort-pulse generation in waveguide laser operating at a wavelength of 2 microns was demonstrated and passively q-switched mode-locked operation was achieved with all absorbers. The material systems that were studied in this work include nanosheet-based absorbers composed of graphene, carbon nanotubes, black phosphorus, transition-metal dichalcogenides, topological insulators and indium tin oxide. By utilizing a uniform few-layer spin coating fabrication technique and by employing a single, identical laser resonator, a direct comparison of the individual characteristics of these materials in the context of short-pulse generation in waveguide lasers was made possible. Each of the individually fabricated and characterized saturable absorbers was placed inside a thulium-doped fluoride glass waveguide chip laser cavity and the resulting output performance was analyzed and contrasted. It was further found that the few-layer spin coating approach enables fine-tuning of the absorber characteristics and that all low-dimensional nanomaterials under investigation can be utilized for ultrashort pulse generation in the 2-micron wavelength range. General guidelines for the design of passively modulated shortpulsed laser oscillators are presented based on those findings. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement